Residual Noise Effects - HP 8901B Operation And Calibration Manual

Model 8901B
Operation
Residual Noise Effects
DESCRIPTION
To make the most accurate peak-modulation measurements, it is necessary to measure and correct the
effects of residual noise, that is, noise not on the baseband signal, but modulating the
RF
carrier. The
following procedure describes the measurement technique.
PROCEDURE
The following procedure enables the user to correct for the effects of residual noise on peak-modulation
measurements.
NOTE
T h i s
procedure applies to sinewave modulation only.
1. Set up and make
a
normal peak-modulation measurement. The displayed measurement result
will
2.
Press the Range Hold key
to
prevent autoranging. If filtering and/or de-emphasis was used in
3. Remove the modulation from the signal and measure the remaining peak-residual noise, Npk, on
4.
Select AVG. Measure the average residual noise, Nav.
5.
Compute
include the signal plus its noise,
(s +
N ) p k .
step 1, make a l l the following measurements with the Same settings.
the carrier.
6. Use the following nomograph to determine the percent, N%, of the peak-residual noise level,
N p k ,
to
be subtracted Erom the original, peak-signal-plus-noise
measurement, (S
+
N ) p k .
7. Compute the corrected, peak modulation
where N % is expressed as a ratio (rather than in 7%).
Residual Noise Effects
3-191